Carbonylation reaction and catalyst therefor

ABSTRACT

A process and novel catalyst for the carbonylation of one or more of alcohols, ethers and ether alcohols to esters and, optionally, to carboxylic acids. The reaction is effected in the vapor state over a solid catalyst comprising a polyoxometalate anion in which the metal is at least one taken from Group V and VI of the Periodic Chart of the Elements complexed with a cation from a member of Group VIIIA of the Periodic Chart of the Elements. Preferably, the catalyst is deposited on a support that is inert to the reaction. The preferred support is silica.

BRIEF DESCRIPTION OF THE INVENTION

Alcohols, ethers and ether alcohols are carbonylated to esters and,optionally, to carboxylic acids, by reaction in the vapor state over asolid catalyst comprising a polyoxometalate anion in which the metal isat least one taken from Group V and VI of the Periodic Chart of theElements (such as molybdenum, tungsten, vanadium, niobium, chromium, andtantalum), complexed with at least one Group VIIIA (of the PeriodicChart of the Elements) cation, such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pdand Pt. Preferably, the catalyst is deposited on a support that is inertto the reaction. The preferred support is silica. Novel carbonylationcatalysts are described.

BACKGROUND TO THE INVENTION

Carbonylation of alcohols and ethers to their corresponding esters is awell known art and is illustrated in Equations 1 and 2 below.

    2ROH+CO→RC(O)OR+H.sub.2 O                           (1)

    ROR'+CO→RC(O)OR'                                    (2)

In addition, alcohols can be carbonylated to carboxylic acids as shownin Equation 3, below.

    ROH+CO→RC(O)OH                                      (3)

Carbonylation of methanol, equations 1 and 3, is a well known reactionand is traditionally carried out in the liquid phase with a catalyst.The catalyst typically comprises a Group VIII metal, a halide promoter(normally some form of iodide) and occasionally a ligand such as PR₃ orNR₃ (R being organic moiety).

The most common catalyst for a liquid phase system is Rh in combinationwith HI/CH₃ I. This catalyst is considered "state of the art" and isdescribed in U.S. Pat. No. 3,769,329. This technology/catalyst isutilized in many commercial processes that generate acetic acid viamethanol carbonylation. The operating conditions are about 180°-200° C.and about 450 psi CO with>95% selectivity to methyl acetate/acetic acid.

Prior to the development of the Rh and HI/CH₃ I system, the reaction wascarried out in a liquid phase system with Co-I catalysts such asdescribed in U.S. Pat. No. 3,060,233. The operating conditions are about200° C. and about 7,000-10,000 psi CO. The product selectivity is about93%. A number of researchers have described the use of Ni-basedcatalysts for the carbonylation reaction. An example is EP 18 927. Thecatalyst of that publication consists of Ni and a combination of ioniciodides (example: KI) and covalent iodides (example: CH₃ I). Thereaction is carried out at about 150° C. and about 800-1,000 psi CO.

All of the liquid phase catalysts that generate methyl acetate/aceticacid at commercially acceptable rates and selectivities require the useof an iodide promoter, typically CH₃ I and/or HI, and high pressure (atleast about 450 psi). The iodides are highly corrosive and necessitatethe use of expensive corrosion resistant materials of construction. Inaddition, separation of the catalyst is a major problem and requiresspecial equipment.

Vapor phase carbonylation of methanol has the advantage of easy productseparation from the catalyst. In most cases, patents describinghomogeneous catalysts also claim that the reaction can be carried out inthe vapor phase [e.g., methanol and an iodide containing compound (CH₃I) are co-fed] with the catalyst supported on a material such as silica(SiO₂) or alumina (Al₂ O₃). Rarely are examples given. The followingdescriptions refer to references which deal only with vapor phasecarbonylation.

A considerable amount of work has been carried out on heterogeneousversions of the Rh/CH₃ I system described above, see for example,Journal of Catalysis (13, p. 106, 1969 and 27, p. 389, 1972). In atypical illustration, Rh is supported on activated carbon and a gaseousmixture of CO, CH₃ OH, and CH₃ I is passed over the catalyst at175°-250° C. and 300 psi. The catalyst is active and high yields ofacetic acid/methyl acetate are obtained. In similar work, Rh isimpregnated on Al₂ O₃ (Krzywicki et. al., Bull. Soc. Chim. France, 5, p.1094, 1975), SiO₂ and TiO₂ (Krzywicki et.al., J. Mol. Cat., 6, p. 431,1979) or zeolite-encapsulated (Schwartz et.al., J. Mol. Cat., 22, p.389, 1984). In both cases CH₃ OH and CH₃ I are co-fed to the reactorcontaining the catalyst. It should be noted that in all these examplesCH₃ I is required in order for the carbonylation reaction to work.

In JA 59139330, the carbonylation catalyst consist of Ni supported onactivated carbon. The reaction is carried out at 200°-300° C. and 150psi with a feed mixture of CO:CH₃ OH:CH₃ I=5:1:0.01. At 300° C., themethanol conversion is 100% and the acetic acid/methyl acetateselectivity is>95%. In JA 59172436 the same catalyst is utilized tocarbonylate dimethyl ether. In DE 3323654 a CH₃ OH/CH₃ I feed mixture iscarbonylated with a Pd-Ni catalyst supported on activated carbon. Thereaction is carried out at 300° C. and 1 atm CO.

Gates, J. Mol. Cat., 3, p. 1, 1977, reports that Rh impregnated incrosslinked polystyrene is a vapor phase catalyst for the carbonylationof CH₃ OH. Catalyst activity and stability are low. In JA 56104838 andJA 56104839 various Group VIII metals (Rh, Ni, Pd, Ru, Co) and rareearth metal oxides (Cs, La) are supported on silica. Methanolcarbonylation is carried out at 150°-200° C. and 1-5 atm CO, and methylacetate selectivity is high. In these examples, CH₃ I is not utilized inthe reaction feed.

Vapor phase processes that need CH₃ I as a promoter will be corrosiveand require expensive materials of construction. In addition, extensiveseparation/purification procedures are required in order to removeiodides from the product.

Heteropoly acids are well known compounds. The name "heteropoly acids"refers to a broad class of compounds of varying composition. A goodgeneral review of their physical properties is given by Tisgdinos inClimax Molybdenum Company, Bulletin Cdb-12a, 1969.

The use of heteropoly acids in many areas of catalysis is well knownincluding dehydration of alcohols, Friedel-Crafts type reactions,oxidative dehydrogenation and partial oxidation of organic compounds.For examples see Matveev, et. al., J. Mol. Cat., 38, 345, 1986, Dun, et.al., Applied Catalysis, 21, 61, 1986, Nomiya, et. al., Bull. Chem. Soc.Jap., 53, 3719, 1980, and Izumi, et. al. J. Mol. Cat., 18, 299, 1983.Recently, much attention has been given to heteropoly acids as acatalyst for the conversion of methanol into hydrocarbons:

    xCH.sub.3 OH→CH.sub.2 ═CH.sub.2 +CH.sub.3 CH═CH.sub.2 +other hydrocarbons                                              (4)

See Moffat, et. al., J. of Cat., 77, p. 473, 1982, Ono, et. al. Bull.Chem. Soc. Jap., 55, p. 2657, 1982, and Moffat, et.al., J. of Cat., 81,p. 61, 1983. This reaction is carried out in the vapor phase (300°-375°C.) and the products include ethylene, propylene and saturated C₁₋₅hydrocarbons. Reaction 4 dominates the known chemistry of reactions ofmethanol in the presence of heteropoly acids. It was thereforeunexpected to find that methanol carbonylation could be carried out withheteropoly acids.

Hetero polyacids and polyoxometalate anions constitute well recognizedcompositions. They embrace the well-known complexes calledisopolyoxoanions and heteropolyoxoanions. They are represented by thegeneral formulas¹

THE INVENTION

This invention relates to a novel vapor phase carbonylation process ofalcohols and ethers which utilizes polyoxometalate anions as thecatalysts and to the catalysts. The process involves the carbonylationof one or more of alcohols, ethers, and ether alcohols to esters and,optionally, to carboxylic acids, by reaction thereof in the vapor stateover a solid catalyst comprising a polyoxometalate anion in which themetal is at least one taken from Group V and VI of the Periodic Chart ofthe Elements complexed with a cation from a member of Group VIIIA of thePeriodic Chart of the Elements.

The process of the invention, in a preferred embodiment, involves thecarbonylation of one or more of alcohols, such as mono- and polyhydricalcohols, alkylethers, such as alkyl or alkylene mono- and polyethers,and alkyl ether alcohols to alkyl alkane monoesters and diesters and,optionally, to alkane monocarboxylic or dicarboxylic acids, by reactionin the vapor state over a solid catalyst comprising a polyoxometalateanion in which the metal is at least one taken from Group V and VI ofthe Periodic Chart of the Elements (such as molybdenum, tungsten,vanadium, niobium, chromium, and tantalum), complexed with at least oneGroup VIIIA (of the Periodic Chart of the Elements) cation, such as Fe,Ru, Os, Co, Rh, Ir, Ni, Pd and Pt. Preferably, the catalyst is depositedon a support that is inert to the reaction. The preferred support issilica.

The invention also embraces solid catalysts for the carbonylation of oneor more of alcohols, ethers and ether alcohols to esters and,optionally, to carboxylic acids, by reaction thereof in the vapor state.The carbonylation catalysts comprise a polyoxometalate anion in whichthe metal is at least one taken from Group V and VI of the PeriodicChart of the Elements (such as molybdenum, tungsten, vanadium, niobium,chromium, and tantalum), complexed with at least one Group VIIIA (of thePeriodic Chart of the Elements) cation, such as Fe, Ru, Os, Co, Rh, Ir,Ni, Pd and Pt. The preferred catalyst is deposited on a support which isinert to the reaction. The preferred support is silica, especially ahigh surface area silica.

DETAILS OF THE INVENTION

The invention is directed to a process of converting alcohols and ethersto carboxylic acids and esters by the carbonylation of the alcohols andethers with carbon monoxide in the presence of a metal ion exchangedheteropoly acid supported on an inert support. The invention alsoembraces novel carbonylation catalysts.

The alcohols and ethers that may be carbonylated by the process of theinvention include any alcohol and ether compound or combination of thetwo. They are preferably exemplified by alcohols and ethers in which analiphatic carbon atom is directly bonded to an oxygen atom of either analcoholic hydroxyl group in the compound or an ether oxygen in thecompound. Such compounds may contain aromatic groups.

The preferred alcohols and ethers that may be carbonylated by theprocess of the invention include alkanols of 1 to about 20 carbon atoms,alkane polyols of 2 to about 24 carbon atoms, alkyl monoethers of 2 toabout 20 carbon atoms, alkyl alkylene polyethers of 4 to about 40 carbonatoms and alkoxyalkanols of 3 to about 20 carbon atoms.

Illustrative of suitable alcohols and ethers that may be carbonylatedaccording to the process of the invention are:

    __________________________________________________________________________    CH.sub.3 OH     CH.sub.3 CH.sub.2 OH                                          CH.sub.3 CH.sub.2 CH.sub.2 OH                                                                 CH.sub.3 CH(OH)CH.sub.3                                       CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 OH                                                        CH.sub.3 CH.sub.2 (CH.sub.3)CHOH                              CH.sub.3 (CH.sub.3)CHCH.sub.2 OH                                                              CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 OH               CH.sub.3 CH.sub.2 CH.sub.2 CH(OH)CH.sub.3                                                     CH.sub.3 CH.sub.2 CH(OH)CH.sub.2 CH.sub.3                     CH.sub.3 CH.sub.2 CH(OH)CH.sub.2 CH.sub.3                                                     CH.sub.3 (CH.sub.3)C(OH)CH.sub.2 CH.sub.3                     CH.sub.3 (CH.sub.3)CHCH(OH)CH.sub.3                                                           CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 OH      CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CH(OH)CH.sub.3                                            CH.sub.3 CH.sub.2 CH.sub.2 CH(OH)CH.sub.2 CH.sub.3            CH.sub.3 CH.sub.2 CH.sub.2 (CH.sub.3)CHCH.sub.2 OH                                            CH.sub.3 CH.sub.2 (CH.sub.3)CHCH.sub.2 CH.sub.2 OH            CH.sub.3 CH.sub.2 (CH.sub.3 CH.sub.2)CHCH.sub.2 OH                                            CH.sub.3 (CH.sub.3 CH.sub.2)CHCH.sub.2 CH.sub.2 OH            CH.sub.3 (CH.sub.2).sub.8 OH                                                                  CH.sub.3 (CH.sub.2).sub.17 OH                                 CH.sub.3 (CH.sub.2).sub.8 (CH.sub.3)CH.sub.2 OH                                               C.sub.6 H.sub. 11 OH                                          C.sub.6 H.sub.11 CH.sub.2 OH                                                                  C.sub.6 H.sub.5 CH.sub.2 OH                                   o-C.sub.6 H.sub.5 (CH.sub.2 OH).sub.2                                                         p-C.sub.6 H.sub.5 (CH.sub.2 OH).sub.2                         1,2,4-C.sub.6 H.sub.5 (CH.sub.2 OH).sub.3                                                     p-C.sub.6 H.sub.5 (CH.sub.2 CH.sub.2 OH).sub.2                HOCH.sub.2 CH.sub.2 OH                                                                        HOCH.sub.2 CH.sub.2 CH.sub.2 OH                               HOCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 OH                                                      HO(CH.sub.2).sub.4-17 CH.sub.2 OH                             (HOCH.sub.2).sub.4 C                                                                          1,4-HOC.sub.6 H.sub.4 CH.sub.2 OH                             CH.sub.3 OCH.sub.3                                                                            CH.sub.3 CH.sub.2 OCH.sub.3                                   CH.sub.3 CH.sub.2 OCH.sub.2 CH.sub.3                                                          CH.sub.3 CH.sub.2 CH.sub.2 OCH.sub.3                          CH.sub.3 CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.3                                                 CH.sub.3 CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 CH.sub.3        CH.sub.3 CH(OCH.sub.3)CH.sub.3                                                                CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 OCH.sub.3                 CH.sub.3 CH.sub.2 (CH.sub.3)CHOCH.sub.3                                                       CH.sub.3 (CH.sub.3)CHCH.sub.2 OCH.sub.2 CH.sub.3              CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 OCH.sub.3                                        CH.sub.3 CH.sub.2 CH.sub.2 CH(OCH.sub.2 CH.sub.2 OCH.sub.3                    )CH.sub.3                                                     CH.sub.3 CH.sub.2 CH(OCH.sub.3)CH.sub.2 CH.sub.3                                              CH.sub.3 CH.sub.2 CH(OCH.sub.2 CH.sub.3)CH.sub.2 CH.sub.3                     .                                                             CH.sub.3 (CH.sub.3)C(OCH.sub.2 CH.sub.3)CH.sub.2 CH.sub.3                                     CH.sub.3 (CH.sub.3)CHCH(OCH.sub.2 CH.sub.2 OCH.sub.2                          CH.sub.3)CH.sub.3                                             CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 OCH.sub.3                               CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CH(OCH.sub.3)CH.sub.3                     N                                                             CH.sub.3 CH.sub.2 CH.sub.2 CH(OCH.sub.3)CH.sub.2 CH.sub.3                                     CH.sub.3 CH.sub.2 CH.sub.2 (CH.sub.3)CHCH.sub.2 OCH.sub.3                     O                                                             CH.sub.3 CH.sub.2 (CH.sub.3)CHCH.sub.2 CH.sub.2 OCH.sub.3                                     CH.sub.3 CH.sub.2 (CH.sub.3 CH.sub.2)CHCH.sub.2 OCH.sub.3                     N                                                             CH.sub.3 (CH.sub.3 CH.sub.2)CHCH.sub.2 CH.sub.2 OCH.sub.3                                     CH.sub.3 (CH.sub.2).sub.8 OCH.sub.3                           CH.sub.3 (CH.sub.2).sub.17 OCH.sub.3                                                          CH.sub.3 (CH.sub.2).sub.8 (CH.sub.3)CH.sub.2 OCH.sub.3        C.sub.6 H.sub.11 OCH.sub.3                                                                    C.sub.6 H.sub.11 OC.sub.6 H.sub.11                            C.sub.6 H.sub.11 CH.sub.2 OC.sub.6 H.sub.5                                                    C.sub.6 H.sub.5 OCH.sub.3                                     C.sub.6 H.sub.5 OH                                                                            C.sub.6 H.sub.5 CH.sub. 2 OCH.sub.3                           o-C.sub.6 H.sub.5 (CH.sub.2 OCH.sub.3).sub.2                                                  p-C.sub.6 H.sub.5 (CH.sub.2 OCH.sub.3).sub.2                  1,2,4-C.sub.6 H.sub.5 (CH.sub.2 OCH.sub.3).sub.3                                              CH.sub.3 (OCH.sub.2 CH.sub.2).sub.1-30 OCH.sub.3              C.sub.6 H.sub.5 CH.sub.2 OCH.sub.2 CH.sub.2 CH.sub.2 OH                                       CH.sub.3 OCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 OH              CH.sub.3 O(CH.sub.2).sub.4-17 CH.sub.2 OH                                                     (CH.sub.3 OCH.sub.2).sub.4 C                                  sym-CH.sub.3 OC.sub.6 H.sub.4 CH.sub.2 OH                                                     CH.sub.3 (OCH.sub.2 CH.sub.2).sub.1-30 OH                     (CH.sub.3 OCH.sub.2).sub.2 (HOCH.sub.2).sub.2 C                                               1,4-CH.sub.3 OCH.sub.2 C.sub.6 H.sub.4 CH.sub.2 OCH.sub.3     __________________________________________________________________________

The process of the invention involves providing the alcohol and/ether inthe vapor state and passing the vapor over a bed containing the solidcatalyst comprising a polyoxometalate anion in which the metal is atleast one taken from Group V and VI of the Periodic Chart of theElements (such as molybdenum, tungsten, vanadium, niobium, chromium, andtantalum), complexed with at least one Group VIIIA (of the PeriodicChart of the Elements) cation, such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pdand Pt. The temperature at which the reaction is effected is not seen tobe narrowly critical. A temperature between about 100° C. and about 350°C. is usable. Preferably, the temperature of the reaction is betweenabout 125° C. and about 325° C., and temperatures between about 150° C.and about 300° C. are most preferred.

The reaction pressure accommodates the requirement that the reactants befed to the reactor in the vapor state. However, the pressure at whichthe reaction may be carried out may range from about 1 atmosphere toabout 1,000 atmospheres, with pressures of greater than 1 atmosphere toabout 35 atmosphere being preferred. The particular reactants and therate of reaction will impact on the pressure of the reaction zone.

The reaction zone is where the catalyst is located. The reaction may becarried out in a tubular reactor using a fixed bed of the catalyst. Thereactants may be fed to the catalyst by feeding down or up, or acombination of both, to a fixed bed located in an upright tubularreactor. It is preferred to use a reactor design that operates by plugflow and causes the minimal turbulence in the reaction zone. Thereaction may be effected in a dynamic bed of the catalyst. In such areaction, the bed of catalyst is moving such as in the case of a fluidbed of the catalyst.

The gas hourly space velocity³ of the reactants through the reactionzone may be over a broad range. For example, the GHSV may range fromabout 50 to about 50,000 hr.⁻¹, preferably from about 900 to about25,000 hr.⁻¹ The liquid hourly space velocity⁴ to the reactor when thefeed is vaporized within the reactor may range from about 0.01 to about10 hr.⁻¹

Where the alcohol, ether and/or the ether alcohol reactant is a higherboiling material not easily vaporized it can be diluted with a lowerboiling nonreactive solvent or diluent and thus transported over thesolid catalyst. The degree of dilution in some cases can be quiteextreme and of course, such conditions will adversely affect the cost ofcarbonylation. Suitable solvents and diluents include aliphatic andaromatic hydrocarbons, halogenated hydrocarbons, esters, ketones, andthe like.

The invention involves a new family of catalysts for carrying out thecarbonylation reactions herein described such as the carbonylation ofmethanol or dimethyl ether to methyl acetate/acetic acid. The generalformula of a preferred form of the heteropoly acid used in the practiceof the invention is M[Q₁₂ PO₄₀ ] where M is a Group VIII metal or acombination of Group VIII metals, Q is one or more of tungsten,molybdenum, vanadium, niobium, chromium, and tantalum, P is phosphorus,and O is oxygen. In a particularly preferred embodiment of theinvention, Q is tungsten or molybdenum or a mixture of the two. Thepreferred catalyst is derived from heteropoly acids of the formula H₃W₁₂ PO₄₀ xH₂ O. They are acids and generate H⁺.

    H.sub.3 W.sub.12 PO.sub.40 →W.sub.12 PO.sub.40.sup.-3 +3H.sup.+(5)

The preferred catalysts comprise metal ion exchanged heteropoly acids ofthe general formula M[W₁₂ PO₄₀ ] where M is as defined above, W istungsten, and P and O are as defined above supported on a SiO₂ support.The carbonylation reaction is carried out in the vapor phase. A widevariety of catalysts were screened. The preferred catalysts are thosewhere M is Rh, Rh/Pd combinations, Ir, Ir/Rh combinations, Ir/Pdcombinations and Ir/Co combinations.

H₃ W₁₂ PO₄₀ can be chemically modified in several ways. The moststraight forward approach is to exchange the acidic protons with a metalion:

    H.sub.3 W.sub.12 PO.sub.40 +M.sup.+ →M.sub.3 W.sub.12 PO.sub.40 +3H.sup.+                                                 (6)

Any metal ion M⁺ or a combination of ions capable of satisfying theheteropoly acid valence requirements can be utilized. Removal of all ofthe H+ is not required. For example, the reaction with Co⁺² would yield:

    H.sub.3 W.sub.12 PO.sub.40 +Co.sup.+2 →H[CoW.sub.12 PO.sub.40 ]+2H.sup.+                                                (7)

These catalyst compositions are based on idealized stoichiometries suchas that shown by equation (7) immediately above. The exact structure andcomposition of the ultimate catalyst (i.e., the composition effectingthe catalytic activity as contrasted with the starting heteropoly acid)is not known. The catalyst structure may exist as monomers, dimers andso forth. The waters of hydration are not known and are not included inthe catalyst formulas.

All of the M[W₁₂ PO₄₀ ]/SiO₂ catalysts utilized herein as catalystprecursors were prepared in a similar manner, a typical example is asfollows:

Under N₂ at room temperature, RhCl₃.H₂ O (0.47 g., 1.8 mmoles) wasdissolved in 50 milliliters of methanol and stirred for 0.5 hr. H₃ W₁₂PO₄₀ (15-20 wt. % water, 6.5 g., 1.8 mmoles) was added and this solutionwas stirred for 1.0 hour. To the solution was added 3.9 g. of grade 12silica gel (SiO₂) and the resulting slurry was stirred for an additional4.0 hours. The methanol was then removed at 80° C. under vacuum yieldinga red powder. If needed, the flask was further heated with a heat gununtil the powder was free flowing. The material was placed in a vial andstored under N₂. The empirical formula of the composition is Rh[W₁₂ PO₄₀]/SiO₂.

Some of the M[W₁₂ PO₄₀ ] catalysts were prepared with metal nitratesalts. No difference in catalytic activity was seen between Rh[W₁₂ PO₄₀] prepared from chloride, nitrate or AcAc (acetylacetonate) containingRh salts. H₃ [Mo_(x) W_(y) PO₄₀ ] acids were prepared by the procedureof J. Bailar, Inorganic Synthesis, 1, p. 132, (1939) and Na₈ [Rh₂ W₁₂O₄₂ ] was prepared by procedures analogous to Na₈ [Co₂ W₁₂ O₄₂ ] asreported by L. Baker and T. McCutcheon, J. Am. Chem. Soc., 78, p. 4503,(1956).

As illustrated above, the heteropoly acid is impregnated on the supportusing conventional procedures. The choice of the support is notappreciated to be limiting factor in the operation of the invention. Thelimited experience with the selection of supports relative to thesupports effect on the activity of the catalyst suggests that thesupport should have a reasonably high surface area. It is preferred thatthe heteropoly acid be deposited on an inorganic support that has arelatively high surface area, such as a surface area of at least about100 square meters per gram determined by the BET method. In thepreferred embodiment of the invention, the surface area of the supportonto which the heteropoly acid is deposited, and in contact with, has asurface area of at least about 200 square meter per gram, mostpreferably at least about 250 square meter per gram. Typical supportmaterials suitable for the invention are the silicas, thegamma-aluminas, the titanias, the alumina silicates, the high surfacearea clays, and the like. Particularly desirable are the mixed compositesupports in which the high surface area support is deposited over alower surface area support. For example, a silica gel deposited andcured on the surface of an alpha-alumina provides the high surface areafor the subsequent deposition of the heteropoly acid onto the silica gelcoating and the thermal stability provided by the low surface areaalpha-alumina.

The impregnation step simply involves the coating of the support withthe heteropoly acid and then drying the coating on the support to fixit. The drying temperature is not narrowly critical and can range fromabout 100° C. to about 600° C. for a period of about 5 seconds to about8 hours. The lower the temperature, the longer will be the heatingperiod and the higher the temperature, the shorter will be the heatingperiod.

The most commercially interesting reactants are methanol and dimethylether. The products are methyl acetate and acetic acid. The methylacetate selectivity can be at least 95% at 225° C. and 1 atm. totaloperating pressure.

    2CH.sub.3 OH+CO→CH.sub.3 C(O)OCH.sub.3 +H.sub.2 O   (8)

    CH.sub.3 OCH.sub.3 +CO→CH.sub.3 C(O)OCH.sub.3       (9)

In addition, methanol can be carbonylated to acetic acid as shown inEquation 10, below.

    ROH+CO→RC(O)OH                                      (10)

In the case of the carbonylation of methanol, dehydration occurs as aside reaction due to the acidic nature of the heteropoly acid catalystsof the invention, e.g., the M[W₁₂ PO₄₀ ] catalysts. Dehydration resultsin the formation of dimethyl ether as shown by equation 11.

    2CH.sub.3 OH→CH.sub.3 OCH.sub.3 +H.sub.2 O          (11)

Since dimethyl ether is carbonylated to methyl acetate (equation 6) itcan be recycled back to the reactor with no loss in methanol efficiency.Thus, the feed to the reactor can comprise methanol, dimethyl ether or acombination of both.

In the examples which follow, the GHSV=900 hr¹ and the LHSV=0.15 hr¹.The reactor was a clean 1/4" stainless steel tube packed with glasswool, 2 milliliter of catalyst and additional glass wool. The tube wasplaced in an aluminum block surrounded by a heater and connected to thefeed and exit lines. The CO flow was started, the temperature of thefeed/exit lines adjusted to 160° C. and the reactor taken to the desiredtemperature. At temperature the methanol feed was started and the systemwas allowed to equilibrate 0.5 hr. Each experiment was normally carriedout for 6 hr. The gas stream exiting the reactor was analyzed with a HP5830 gas chromatograph equipped with a TC detector and a 10'×1/8" columnpacked with Poropak Super Q. The following program was used: temp 1=50°C., time 1=0 min., rate=15 degrees/min., temp 2=225° C., time 2=20 min.

EXAMPLES 1-9

The various MW₁₂ PO_(40/) SiO₂ compounds listed in Table 1 below wereprepared on a silica support having a surface area of about 683 m² /gramaccording to the procedure described above and examined as catalysts forthe carbonylation of methanol. The experiments were carried out at 225°C. and 1 atm. with LHSV=0.15 hr⁻¹ and GHSV=900 hr⁻¹. The results arelisted in Table 1. The reported catalyst compositions are idealizedstoichiometries.

                  TABLE 1                                                         ______________________________________                                                       Product Yield                                                  Ex. No.  Catalyst    MeOH     DME   MeOAc                                     ______________________________________                                        1        IrW.sub.12 PO.sub.40                                                                      8.0      52.0  40.0                                      2        RhW.sub.12 PO.sub.40                                                                      17.0     49.0  34.0                                      3        HPdW.sub.12 PO.sub.40                                                                     0.0      92.0  8.0                                       4        HMnW.sub.12 PO.sub.40                                                                     0.0      96.0  4.0                                       5        HCoW.sub.12 PO.sub.40                                                                     5.0      92.0  3.0                                       6        HNiW.sub.12 PO.sub.40                                                                     7.0      90.0  3.0                                       7        FeW.sub.12 PO.sub.40                                                                      7.0      92.0  1.0                                       8        HZnW.sub.12 PO.sub.40                                                                     0.0      99.0  1.0                                       9        ThW.sub.12 PO.sub.40                                                                      6.0      93.0  1.0                                       ______________________________________                                    

EXAMPLE 10

The catalyst of Example 2 (RhW₁₂ PO₄₀) was supported on alumina,florisil, and alundum supports instead of SiO₂. The carbonylationreaction was carried out exactly as Examples 1-9. Small amounts ofmethyl acetate were formed.

EXAMPLES 11-18

Bimetallic compounds, M1M2W₁₂ PO₄₀ deposited on SiO₂, where M1M2 is acombination of two metals (M1+M2), were examined as catalysts. Thecatalysts were prepared such that the mole ratio of M1:M2:H₃ W₁₂ PO₄₀=1:1:2. The exact composition of these materials was not determined. Thecarbonylation reaction was carried out as described in Examples 1-9. Theresults are given in Table 2 below.

                  TABLE 2                                                         ______________________________________                                                      Product Yield                                                   Ex. No.  M1      M2     MeOH    DME   MeOAc                                   ______________________________________                                        11       Rh      Ir     4.0     52.0  44.0                                    12       Rh      Mn     3.0     62.0  35.0                                    13       Rh      Pd     3.0     38.0  59.0                                    14       Rh      Co     6.0     68.0  26.0                                    15       Ir      Co     3.0     39.0  58.0                                    16       Ir      Mn     5.0     41.0  54.0                                    17       Ir      Pd     2.0     40.0  58.0                                    18       Pd      Mn     8.0     84.0  8.0                                     ______________________________________                                    

EXAMPLES 19-23

In these example, Na₈ [Rh₂ W₁₂ O₄₂ ] without deposition on silicasupport (catalyst "A") and deposited on silica support (catalyst "B")were examined as carbonylation catalysts. The runs were carried outsimilar to Example 1-9. The results are reported in Table 3 below.

                  TABLE 3                                                         ______________________________________                                                         Product Yield                                                Ex. No.                                                                              Catalyst  Temp. °C.                                                                        MeOH  DME   MeOAc                                  ______________________________________                                        19     A         225       99.0  0.0   1.0                                    20     A         250       98.0  0.0   2.0                                    21     A         275       96.0  0.0   4.0                                    22     B         225       87.0  0.0   13.0                                   23     B         275       85    0.0   15.0                                   ______________________________________                                    

EXAMPLES 24-27

Heteropoly acids containing both W and Mo were synthesized according tothe following reaction:

    6Na.sub.2 WO.sub.4 +6Na.sub.2 MoO.sub.4 +Na.sub.2 HPO.sub.4 +26HCl→H.sub.3 Wo.sub.6 Mo.sub.6 PO.sub.40 +26NaCl+12H.sub.2 O

The reaction is general therefore H₃ W_(x) Mo_(y) PO₄₀, where x+y=12,were prepared by adjusting the ratios of the reagents. The H₃ W_(x)Mo_(y) PO₄₀ acids were then exchanged with Rh and deposited onto SiO₂ togive RhW_(x) Mo_(y) PO₄₀ /SiO₂ catalysts. The catalysts were examined at225° C., 1 atm CO and GHSV=900 hr⁻¹. The results are given in Table 4below.

                  TABLE 4                                                         ______________________________________                                        Catalyst                                                                      RhW.sub.x Mo.sub.y PO.sub.40                                                  Example No.                                                                              x         y      MeOAc Yield %                                     ______________________________________                                        24         8         4      16.0                                              25         6         6      11.0                                              26         4         8      8.0                                               27         2         10     4.0                                               ______________________________________                                    

EXAMPLES 28-33

In these examples methanol was replaced by dimethyl ether. The reactionwas carried out at 225° C. and 1 atm. CO with the catalysts reported inTable 5 below. Each of the catalysts were deposited and supported onhigh surface area silica, as characterized above.

                  TABLE 5                                                         ______________________________________                                                        Product Yield                                                 Ex. No. Catalyst      MeOH     DME   MeOAc                                    ______________________________________                                        28      IrW.sub.12 PO.sub.40                                                                        0.0      87.0  13.0                                     29      RhW.sub.12 PO.sub.40                                                                        0.0      84.0  16.0                                     30      HCoW.sub.12 PO.sub.40                                                                       1.0      98.0  1.0                                      31      HNiW.sub.12 PO.sub.40                                                                       2.0      96.0  1.0                                      32      Ir--Pd[W.sub.12 PO.sub.40 ].sup.5                                                           0.0      89.0  11.0                                     33      Rh--Pd[W.sub.12 PO.sub.40 ].sup.6                                                           0.0      99.0  1.0                                      ______________________________________                                         In the above:                                                                  1. "Me" stands for methyl and "Ac" stands for acetate.                       2. "Product yield": Unless otherwise noted, the only products observed in     the off gas stream were methanol (MeOH), dimethyl ether (DME), and methyl     acetate (MeOAc). The product yield for each component is given by             Product Yield = P/Combined weight of MeOH + MeOAc + DME                       where P is the weight of methanol, methyl acetate or dimethyl ether. Note     that this is not product selectivity. Since methanol and dimethyl ether       can be recycled back to methyl acetate the selectivity to methyl acetate      approaches 100%.                                                              .sup.5 Same catalyst as used in Example 17 above.                             .sup.6 Same catalyst as used in Example 13 above.                        

I claim:
 1. A process for the carbonylation of one or more alcohols,ethers and ether alcohols to esters and, optionally, to carboxylicacids, by reaction thereof in the vapor state over a solid catalystcomprising a polyoxometalate anion in which the metal is one or moremetals selected from the group consisting of molybdenum, tungsten,vanadium, niobium, chromium, and tantalum, complexed with a cation ofone or more metals selected from the group consisting of Fe, Ru, Os, Co,Rh, Ir, Ni, Pd and Pt.
 2. The process of claim 1 wherein the catalyst isdeposited on a support that is inert to the reaction.
 3. The process ofclaim 2 wherein the support is a member of the group consisting ofsilicas, the gamma-aluminas, the titanias, the alumina silicates, andthe high surface area clays.
 4. The process of claim 2 wherein thesupport is a mixed composite supports in which a high surface areasupport is deposited over a lower surface area support.
 5. The processof claim 4 wherein the support is silica.
 6. The process of claim 5wherein the alcohol is methanol.
 7. The process of claim 5 wherein theether is dimethyl ether.
 8. The process of claim 5 wherein the ester ismethyl acetate.
 9. The process of claim 5 wherein the surface area ofthe silica is at least about 100 square meters per gram.
 10. The processof claim 5 wherein the surface area of the silica is at least 200 squaremeter per gram.
 11. The process of claim 5 wherein the surface area ofthe silica is at least 250 square meter per gram.
 12. The process ofclaim 1 wherein the temperature of the reaction is about 100° C. toabout 350° C.
 13. The process of claim 2 wherein the temperature of thereaction is about 100° C. to about 350° C.
 14. The process of claim 5wherein the temperature of the reaction is about 100° C. to about 350°C.